Small high speed propfans exhibit relatively high efficiency when employed as an aircraft propulsion system. However, in certain missile applications, the propfan is larger in diameter than the missile and cannot be stored as completely or launched as easily as a turbo jet or turbo fan powered missile.
One solution to the aforesaid problem as taught in application Ser. No. 305,164 filed Feb. 2, 1989, and assigned to the assignee of the present invention, is to hinge the propeller blade so that it can be folded to a position extending generally parallel to the thrust axis of the propulsion system. A hinge is provided near the blade root having a hinge line extending at a right angle to the axis of rotation of the blade. However, the aforesaid solution to the problem of propeller folding is aerodynamically inefficient and, in addition, exacerbates the problem of radar signature due to the geometry of such a folding mechanism.
Thus, although the aforesaid blade folding system solves the storage problem, it does not present a total solution to the problem of applying a propfan to a missile since it exhibits relatively poor aerodynamic characteristics and a poor radar signature in the run condition.